[rancid] Foundry/Brocade addition - show media

[Roman Hochuli]

Hello Chris

> This adds `show media` and `show media validation` to 'francid' which
> will give useful information about which optics are installed in a
> device. Tested on a Brocade ICX 6650 and Brocade CER 2024.
> 
>     http://falz.net/static/francid-media.diff

I like the idea of keeping track of optics. But what output should "show
media validation" produce? I tried this on a bunch of devicetypes
(rx/icx/fcx/fesx/mlxe/xmr) and none of them support that command.

-- 
Best regards,
Roman Hochuli
Operations Manager

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